1. Field of the Invention
The present invention relates to a metal-clad laminate having a film (which film is hereinafter referred to as a thermoplastic liquid crystal polymer film) including a thermoplastic polymer capable of forming an optically anisotropic melt phase (which thermoplastic polymer is hereinafter referred to as a thermoplastic liquid crystal polymer), and a method for producing such metal-clad laminate. More specifically, the metal laminate obtained in accordance with the present invention has not only excellent properties such as low moisture absorbability, heat resistance, chemical resistance and electrical properties deriving from the thermoplastic liquid crystal polymer film, but also excellent dimensional stability and is useful as materials for a flexible electric wiring board and for a circuit board on which semiconductor devices is mounted.
2. Description of the Related Art
In recent years, demands for scale reduction and weight reduction of portable electronic devices such as mobile communication devices have come to be pressing, and high density mounting has come to be increasingly expected. In accordance with the demands, use has been made of multi-layered wiring boards, reduced wiring pitches, fine via holes, and small-size multiple-pin IC packages and, along therewith, the scale reduction and surface mounting of passive elements such as capacitors and resistors are taking place. In particular, as an effective approach, there have been mentioned techniques of forming those passive elements directly on a surface of and/or inside the printed wiring board or the like and techniques of directly mounting active elements such as IC packages on a surface of the printed wiring board, and these techniques are effective not only to achieve a high density mounting, but to increase the reliability. As a result, requirements for the dimensional stability of the wiring boards have come to be highly developed, that is, the stable rate of change in dimension before and after formation of semiconductor circuits as well as before and after the heating process used to mount the active and/or passive elements has been required. In addition, the necessity to eliminate the anisotropy of the wiring boards has come to be increasing.
The thermoplastic liquid crystal polymer film having excellent properties such as low moisture absorbability, heat resistance, chemical resistance and electrical properties has been rapidly commercialized as a material for an insulation substrate which improves reliability of printed wiring boards.
Hitherto, manufacture of a metal-clad laminate by laminating a thermoplastic liquid crystal polymer film and a metallic sheet together has been carried out by the utilization of a vacuum hot press apparatus. This lamination is conducted by a process in which while the thermoplastic liquid crystal polymer film and the metallic sheet are placed in between two hot plates, the both are thermally compressed to bond them together under a vacuum atmosphere, and this process is called as a vacuum hot press lamination process. In order to obtain the metal-clad laminate excellent in dimensional stability, with this lamination method, the coefficients of longitudinal and transverse thermal expansion of the thermoplastic liquid crystal polymer film used as a raw material must be adjusted to a value approximating to the thermal expansion coefficient of the metallic sheet and by so doing, the anisotropy in dimensional stability can be eliminated. However, since the vacuum hot press lamination process is a sheet-feed type manufacturing process, a large length of time such as material setting time, press work time for one cycle, and time required to remove the material after the press work is necessary to complete production of one metal-clad laminate, and the production rate is therefore lowered. If an attempt is made to improve the machine and equipments so that a number of products can be manufactured all at a time with the production rate increased, the machine and equipments tend to become bulky in size and costly, resulting in increase of the cost. Accordingly, development of a continuous manufacturing method capable of alleviating the foregoing problems has hitherto been desired for.
On the other hand, in order to provide the full features of the thermoplastic liquid crystal polymer film and, further, to bring out the superiority thereof in terms of cost, continuous lamination with the metallic sheet has to be embodied and this has hitherto been deliberated in various fields. By way of example, conditions necessary to improve the adhesive force between the polymer film and the metallic sheet and a technique for improving the mechanical strength (See, for example, the JP Laid-open Patent Publication No. H05-42603.) have been well known in the art. The method of treating a thermoplastic liquid crystal polymer film, particularly a technology concerning the rate of change in dimension upon heating of the thermoplastic liquid crystal polymer film (See, for example, the JP Laid-open Patent Publication No. H08-90570.) has also been well known in the art.